Process of melt-spinning polyacrylonitrile fiber

Abstract

Processes for producing carbon fibre, the filament thereof and pre-oxidized fibre are provided. In one embodiment, the gel spinning of polyacrylonitrile filament is achieved by using small-molecule gelling agent, and the carbon fibre obtained thereby is increased by 15% to 40% in tensile strength and by 20% to 35% in toughness. In another embodiment, the melt spinning process of polyacrylonitrile is conducted by using imidazole type ion liquid as plasticizer, the process reduces environment pollution, is suitable for industrial production and the fibre produced thereby is improved in its strength. In yet another embodiment, polyacrylonitrile pre-oxidized fibre is produced by melt spinning, so low cost and controllable pre-oxidization of polyacrylonitrile can be achieved. In a further embodiment, high strength carbon fibre is manufactured by using polymer thickening agent. In another further embodiment, low cost and controllable pre-oxidization of polyacrylonitrile is achieved by conducting pre-oxidization before spinning, minimizing skin-core structure, so as to produce high performance carbon fibre, and reduce the production cost of carbon fibre greatly.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a divisional application of U.S. patent application Ser. No. 13 / 262,620 filed on Sep. 30, 2011, which is a National Phase of International Application No. PCT / CN2010 / 000036, which was filed on Jan. 11, 2010, and which claims priority to and the benefit of Chinese Patent Application Nos. 200910048603.8 filed on Mar. 31, 2009, 200910052721.6 filed on Jun. 9, 2009, 200910053212.5 filed on Jun. 17, 2009, 200910195794.0 filed on Sep. 17, 2009, and 200910198444.X filed on Nov. 6, 2009, and the disclosures of which are hereby incorporated herein by reference in their entireties.TECHNICAL FIELD[0002]The present invention belongs to the field of processing technology of carbon fibres. In particular, the present invention relates to processes for producing carbon fibre, precursor fibre and pre-oxidized fibre thereof.BACKGROUND ART[0003]Carbon fibre is widely used in high-tech industrial field due to its excellent properties such...

AI Technical Summary

Benefits of technology

The present invention aims to address issues in carbon fibre production by developing processes for producing high-quality precursor fibre, cost-effective pre-oxidized fibre and carbon fibre while reducing environmental pollution.

Problems solved by technology

The low quality of polyacrylonitrile (PAN) based precursor fibre has been a “bottleneck” restricting the development of carbon fibre industry in china for many years.

Compared with precursor fibre produced abroad, homemade precursor fibre has larger fineness, lower strength, larger dispersion coefficient, more defects, cracks and voids, lower crystallinity and orientation, etc, which are serious problems existing during production of precursor fibre.

As far as quality and yield of precursor fibre are concerned, quality is the primary problem at present.

The tensile strength of most carbon fibres produced from homemade precursor fibre is about 3.5 GPa, which can not fulfil the requirement for use at present, therefore its application is limited.

Meanwhile, the poor stability of precursor fibre quality is an obstacle to scale production.

A large amount of toxic or corrosive chemical solvents are required in industrialized wet spinning and dry spinning, and recovery and purification of the used solvents, washing fibres with water and drying, as well as “three wastes” treatment are necessary during production.

However, this method also has the following problems: A. The extrusion pressure of screw is relatively high due to the poor rheological properties of hydrous melts; B. To prevent the surface of fibre from being coarse and microvoids being formed thereon which result in poor mechanical properties of fibre due to too quick water evaporation during coagulation, saturated steam of certain pressure is required to be maintained in the spinning duct, thereby presenting a requirement for devices; C. It is difficult to control the process due to the narrow temperature range for melt spinning of hydrous melt, therefore industrialization of melt spinning of hydrous melt has not been realized yet at present.

Since there is dramatic structural transformation during pre-oxidization, defects are easily caused, resulting in a decrease of the mechanical properties of carbon fibre.

However, such an order will result in the following shortcomings: 1) During pre-oxidization of PAN precursor fibre, uneven morphological structure of fibre will be caused if there is a gradient difference of pre-oxidization degree across the cross-section of fibre, such as common skin-core structure, which will result in uneven radical contraction across the cross-section of fibre and poor preferred orientation and tensile performance, and therefore decrease of properties of final carbon fibre.

2) The pre-oxidization process is very time-consuming, its temperature is high and equipments are complicated, resulting in the improved cost for pre-oxidization and therefore eventually, the whole cost of manufacturing carbon fibre are substantially increased.

As the pre-oxidization reaction continues, compact thin layer with ladderlike structure is formed on the surface of fibre at first, blocking the diffusion of oxygen, and then a skin-core structure is formed, resulting in defects of carbon fibre.

However, the equipments for this process are extremely complicated, the temperature is difficult to control and the cost is high.

The key for lowering production cost is shorten the time for pre-oxidization which causes easily skin-core structure and subsequently larger voids and defects during carbonizing procedure, thereby resulting in decrease of mechanical properties of carbon fibre.

Skin-core structure is not obvious by lowering temperature and prolonging time of pre-oxidization, which is beneficial to properties of carbon fibre, however, also lowers the production efficiency.

Thus an excellent process for pre-oxidization has not been developed yet.

During the production of carbon fibre (or graphite fibre), especially carbon fibre obtained by using PAN precursor fibre as starting material, the formation of voids on surface is caused by defects of precursor fibre itself and evenness problems during production.

Repairing voids on surface has been concerned in carbon fibre production field, but there is not good means for it until now, and the only way at present is to sacrifice monofilaments with voids, therefore the overall mechanical properties of carbon fibre are substantially decreased.

However, the equipments for this process are very complicated and costly, uneasily to handle and the efficiency is low.

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